I am using IOMMU along with VFIO to passthrough a VGA card on both of my setups. Everything worked fine till kernel 4.1, but after the introduction of "iommu/vt-d: Make root entry visible for hardware right after allocation", both the boards no longer boot with "intel_iommu=on" commandline parameter.
The logs show the following:
DMAR: RMRR base: 0x000000bf7e8000 end: 0x000000bf7fffff
DMAR: ATSR flags: 0x0
DMAR: dmar0: Using Queued invalidation
------------[ cut here ]------------
WARNING: CPU: 4: PID: 1 at /home/dhiru1602/linux-git/kernel/watchdog.c:311 watchdog_overflow_callback+0x79/0xa0()
Watchdog detected hard LOCKUP on cpu 4
Modules Linked in:
CPU: 4 PID: 1 Comm: swapper/0 Tainted: G I 4.2.0-iommu-test
The kernel panic occurs very early in the boot process and I was not able to grab the full kernel panic log.
I have reverted the patch and recompiled the kernel. I was able to boot fine on both the boards with intel_iommu=on and I was able to see the IOMMU groups.
On a sidenote, Both the boards have broken interrupt remapping and the vendors have not provided BIOS updates to fix this problem. There was a report for the Intel board made on the Intel Community Forums here:
https://communities.intel.com/thread/44752 but there hasn't been an updated BIOS released by Intel to fix this issue.
Please let me know if more information is needed to diagnose this issue.
--